With the rapid development of the semiconductor IC manufacturing technology, the pattern critical dimension of the integrated circuit chips has scaled down to the deep sub micrometer stage, and accordingly the dimension of the main contaminants (such as particles) which will cause the failure or damage to the ultra-fine circuits on the chip also greatly decreases.
In the IC manufacturing process, during multiple processing steps such as a film deposition step, an etch step and a polishing step, etc., which are usually performed to the semiconductor wafers, contaminants are likely produced. In order to maintain the cleanness of the wafer surface and eliminate the contaminants that deposited on the wafer surface during these processing steps, a cleaning process is required to perform to the wafer surface after each of the processing steps. Therefore, the cleaning process has become a most common step in the IC manufacturing for effectively controlling the contamination level of the wafer surface after each processing step, and achieving the purpose of each processing step.
During a conventional single wafer wet cleaning process for removing the contaminants on the wafer surface, the wafer is positioned on a spin susceptor (such as a spin chuck) and rotated at a certain speed, at the same time a certain cleaning solution is sprayed on the wafer surface to performing cleaning.
However, with the critical dimension of the integrated circuit patterns scaling down, it becomes increasingly difficult to remove the contaminants with a smaller size on the wafer surface by using the conventional single wafer wet cleaning process. Therefore, novel cleaning technologies have been widely applied to the conventional single wet cleaning apparatus for further improving the cleaning effect. Atomization is one of such novel cleaning technologies. During the cleaning process, the atomized particles produce an impact force to the liquid membrane on the wafer surface and form a shock wave spreading rapidly in the liquid membrane. The shock wave acts upon the contaminated particles to accelerate peeling the contaminant particles from the wafer surface, as well as to increase the flow speed of the liquid solution on the wafer surface and prompt a faster removal of the contaminant particles from the wafer surface along with the flow of the liquid solution.
However, the atomized particles produced by the current cleaning device have larger size and higher energy, which is prone to cause problems such as the damage to the surface pattern when being applied in the wafer cleaning process under sub-65 nm and beyond technology. On the other hand, the low utilization of the liquid flow in the conventional cleaning device also leads to an extreme waste of resources.
In order to achieve the purpose of minimizing the damage caused by the liquid particles to the sidewalls and edges of the pattern, enhancing the cleaning quality and efficiency and saving the cost, there exists a need for further reducing the size of the sprayed-out liquid particles and better controlling the moving direction, moving speed, moving trajectory as well as the uniformity of the atomized particles.
On the other hand, with the continuous progress of the semiconductor IC manufacturing technology, the size of the semiconductor device is becoming smaller and smaller, as a result, micro particles may be enough to affect the manufacturing process and the performance of the semiconductor device. However, the traditional fluid cleaning method cannot effectively remove these micro particles due to a relatively static boundary layer that formed between the wafer surface and the cleaning liquid. When the diameter of the particles adhered to the wafer surface is smaller than the thickness of the boundary layer, the flow of the cleaning liquid cannot take effect on the particles.
To solve the above problem, ultrasonic or megasonic cleaning is introduced into the semiconductor cleaning process. The ultrasonic or megasonic energy can generate and collapse the tiny air bubbles in the liquid medium. Upon collapse, the air bubbles release energy and cause vibration to form a high speed shock wave in the liquid membrane on the wafer surface, which reduces the thickness of the boundary layer and exposes the contaminant particles in the flowing clean solution, thereby assisting the removal of the micro particles attached to the wafer surface and cleaning the wafer.
Although the ultrasonic or megasonic cleaning process can improve the removing efficiency of the contaminants, the damage to the patterns on the wafer surface still occurs. Specifically, since the ultrasonic or megasonic energy is propagated in the liquid medium through waves, regions of high ultrasonic or megasonic energy density are formed at specific positions where wave superposition is generated and air bubbles have much higher energy when collapsed than the strength of the pattern structures on the wafer surface, which causes the damage to the patterns.
Therefore, there exists a need to improve the uniformity of the ultrasonic or megasonic energy passing on the wafer surface to effectively control the damage to the pattern structures on the wafer surface and enhance the removal efficiency of the contaminant particles attached on the wafer surface.
Furthermore, during the cleaning process using chemical solutions and ultrapure water, materials of the wafer surface are prone to be damaged or reacted with the solutions. For example, during a DHF cleaning process, firstly a DHF solution is injected on the wafer surface through a spray arm to completely remove the native oxide layer formed on the wafer surface. Then ultra-pure water is injected to wash the wafer surface to remove the residual DHF solution and the reaction products. Finally, a nitrogen gas is injected to dry the wafer surface to complete the whole process. However, during the above process, bare silicon on the wafer surface is easy to be reacted with the oxygen in the cleaning chamber to generate silicon dioxide, which changes the materials on the wafer surface and affects the subsequent processes. Accordingly, the oxygen level in the cleaning chamber should be controlled during the process.
Meanwhile, during the above nitrogen gas drying process, watermark defects may appear on the wafer surface if the process condition is not properly controlled. The main mechanism of the watermark formation is that, the residual water formed on the wafer surface due to incomplete drying during the nitrogen gas drying process dissolves the silicon dioxide reacted from oxygen and the silicon element on the wafer surface to further generate H2SiO3 or HSiO3— deposition, thereby creating a flat watermark after the evaporation of the water. Furthermore, during the above cleaning process, water droplets often appear on the wafer edge due to incomplete drying, which also affects the wafer cleaning quality.
Therefore, during the above process, not only the control of the oxygen level in the cleaning chamber, but also the optimization of the drying process is required to achieve a complete drying for the entire wafer surface.
Moreover, in the single wafer wet cleaning apparatus, chemical liquids and ultrapure water are sprayed to the spinning wafer surface by cleaning components such as liquid pipelines or nozzles that are fixed on the spray arm, to achieve the surface cleaning of the wafer. When the time interval between the cleaning processes is long, preflushing of the pipelines is required to keep fresh cleaning liquid filled in the pipelines and ensure consistent cleaning effects of the cleaning processes. Although the preflushing enables replacement of the residual cleaning liquid in the pipeline, it has little effect on the residual cleaning liquid at the outlet of the pipelines or nozzles. Especially, when the cleaning apparatus is kept in a standby state for a long time, some chemical cleaning liquid with high viscosity may be dried to form irregular-shaped particles, which will be transferred to the wafer surface later by the cleaning liquid in the subsequent cleaning process, causing local defects and product yield rate reduction.
Accordingly, there exists a need for improving cleaning the residual chemical liquid at the outlets of the pipelines or nozzles to ensure the consistency of the cleaning effect.
In addition, the regular cleaning process can only remove the contaminants at the center area of the wafer, not that on the wafer edge. The incomplete removal of the contaminants on the wafer edge may at least result in the following two hazards. On one respect, the contaminants on the wafer edge such as metal ions may diffuse into the center area of the wafer and then contaminates the whole wafer, causing a decline in the manufacturing yield rate. On the other respect, the contaminants on the wafer edge may be transferred to other wafers through the clamping pins, the chuck, the FOUP and so on, causing the contamination to other wafers.
Therefore, there also exists a need to regulate the spay direction of the cleaning liquid to clean the wafer edge, so as to improve the chip manufacturing yield rate.